Scientists have found yet more evidence to suggest that smoking during pregnancy can seriously affect the health of babies.

Researchers in the United States have confirmed that infants are more likely to die from sudden infant death syndrome (SIDS) or cot death if their mother smoked while pregnant.

They have found that smoking during pregnancy may damage key receptors in the brain which control breathing.

They believe this damage could cause infants to stop breathing for no apparent reason after they are born, so called sleep apnoea.

Nicotine exposure

Dr Zili Luo and colleagues at the University of Arizona based their findings on studies on rats.

They divided pregnant rats into two groups. The first group received a dose of a harmless saline solution from the fifth day of their pregnancy right through to delivery, which is at 21 days.

Our advice to parents is that they should not smoke during pregnancy and that includes prospective dads too

Spokeswoman, Foundation for the Study of Infant Deaths

The second group received a dose of nicotine, equivalent to levels found in a human who smokes two packs of cigarettes a day, over the same period.

The researchers subsequently analysed the brains of the newborn rats. They removed their brain stem and spinal cord and placed them in a plasma-like solution containing oxygen.

This enabled them to analyse the breathing rhythm in a highly controlled setting. It also allowed them to add chemicals to the solution to examine how it affects breathing.

The researchers added varying doses of two drugs to this solution. These drugs stimulate GABAa receptors, which control breathing rhythm.

They found that these drugs slowed down breathing in both groups of rats. However, the decrease was sharpest in those rats whose mothers had received nicotine every day.

Dr Luo told delegates at the Experimental Biology 2003 conference in San Diego that the findings suggested that infants whose mothers smoked during pregnancy may also be more likely to be susceptible to reduced rates of breathing and even death.

SIDS occurs most often in infants between the ages of two and four months, while the baby is sleeping. Deaths are usually attributed to the fact that the baby has stopped breathing.

Previous studies have suggested that smoking during pregnancy can increase the risk of SIDS five-fold.

A spokeswoman from the Foundation for the Study of Infant Deaths backed the findings.

"There is no doubt whatsoever that exposing babies to tobacco smoke and nicotine is highly dangerous.

"Our advice to parents is that they should not smoke during pregnancy and that includes prospective dads too. They should never expose babies to tobacco smoke after they are born."